The objectives of the project are 1) to examine the stages of vocal development in normal infants in the first 18 months of life and 2) to find out how each stage relates to its predecessor and to succeeding stages of vocal development. The vocal behaviors of the infants will be studied by means of a descriptive feature system. The features in this system are defined in terms of auditory judgements and acoustic measurements. They are both segmental and suprasegmental in nature. The system is capable of detecting change in the features of vocalization and also of documenting the appearance of new features and new feature sets. The auditory judgements are made by trained listeners. The acoustic measurements are made by means of computer-assisted spectral analyses. These analyses include computor-generated spectrograms and graphic level recordings, pitch extraction, and, in the case of infant vowel data, inverse filtering. The ability of both suprasegmental features, such as temporal organization and pitch contour, and of segmental features, such as consonantal vs. vocalic, and vowel quality, to characterize stages of vocal development will be tested. In addition, if the attempt to characterize vocal development is successful, it is our intention to examine the situational contexts in which characteristic vocal behaviors are produced, and to document nonvocal behaviors that accompany different types of vocal behavior. The project is designed to obtain information for use in assessing speech and language skills in young language-delayed children, and in planning procedures for the treatment of language delay in these children.